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Posted: Sun Nov 13, 2005 7:37 pm
by GaryN
Tony,
I always lay slabs on a 6 sharp sand to one cement wet mix.
Would you envisage this mix causing any problems when using any of the natural stone slabs available (efflorescence being caused for example ?).
Regards
Gary
Posted: Mon Nov 14, 2005 12:53 pm
by Tony McC
There's a deal of consternation amongst the imported stone suppliers as they are faced with more and more problems caused by the bedding ametrails used with their flags. In particular, the wet mix bed technique has been presenting a problem of 'picture framing' where the edges of the flags are absorbing more of the mortar's moisture than the centre, and that moisture seems to be transporting some of the cement content, resulting in distinct staining of the edges.
And, as you noted, there is growing concern regarding the incidence of efflorescence with these flags.
I've heard all sorts of 'fixes' to deal with these problems, but for me, the best solution is to remove the source of the problem, which is the water content of the laying course. It is no coincidence that stone flags laid on a semi-dry mix exhibit far less picture framing and efflorescence. There is less free water to be absorbed by the stone and to transport the cement, so you get fewer problems.
However, I know that some contractors, and many DIYers, find it harder to get a perfect bed using a semi-dry mix than they do with the more forgiving wet mix, so for them I would suggest that they meet half-way and use a moist mix, which has a reduced water content, so less risk of problems, but is sufficiently workable to accommodate the vagaries of these flags.
With the turn of the year, we are coming into the peak season for eff. It's always worse when the daffodils are out, so for anyone considering a flagstone pavement in the next 3-4 months, I would urge them to use a drier/stiffer mix than they would normally, and just see for themselves how much of a difference it can make.
Posted: Mon Nov 14, 2005 7:52 pm
by GaryN
Thanks for your quick reply Tony
Regards
Gary
Posted: Wed Nov 16, 2005 3:25 pm
by mouldmaker
Sage advice that should be bourne in mind when laying concrete paving also!